On Mon, Sep 05, 2022 at 02:29:51PM +0800, Vlastimil Babka wrote: > On 9/5/22 04:55, Feng Tang wrote: > > On Sun, Sep 04, 2022 at 06:58:49PM +0800, Hyeonggon Yoo wrote: > >> On Sun, Sep 04, 2022 at 05:42:33PM +0800, Feng Tang wrote: > >> > On Sun, Sep 04, 2022 at 05:03:34PM +0800, Hyeonggon Yoo wrote: > >> > [...] > >> > > > > > >> > > > > This patch is okay but with patch 4, init_object() initializes redzone/poison area > >> > > > > using s->object_size, and init_kmalloc_object() fixes redzone/poison area using orig_size. > >> > > > > Why not do it in init_object() in the first time? > >> > > > > > >> > > > > Also, updating redzone/poison area after alloc_single_from_new_slab() > >> > > > > (outside list_lock, after adding slab to list) will introduce races with validation. > >> > > > > > >> > > > > So I think doing set_orig_size()/init_kmalloc_object() in alloc_debug_processing() would make more sense. > >> > > > > >> > > > Yes, this makes sense, and in v3, kmalloc redzone/poison setup was > >> > > > done in alloc_debug_processing() (through init_object()). When > >> > > > rebasing to v4, I met the classical problem: how to pass 'orig_size' > >> > > > parameter :) > >> > > > > >> > > > In latest 'for-next' branch, one call path for alloc_debug_processing() > >> > > > is > >> > > > ___slab_alloc > >> > > > get_partial > >> > > > get_any_partial > >> > > > get_partial_node > >> > > > alloc_debug_processing > >> > > > > >> > > > Adding 'orig_size' paramter to all these function looks horrible, and > >> > > > I couldn't figure out a good way and chosed to put those ops after > >> > > > 'set_track()' > >> > > > >> > > IMO adding a parameter to them isn't too horrible... > >> > > I don't see better solution than adding a parameter with current implementation. > >> > > (Yeah, the code is quite complicated...) > >> > > > >> > > It won't affect performance to meaningful degree as most of > >> > > allocations will be served from cpu slab or percpu partial list. > >> > > >> > Thanks for the suggestion! I'm fine with it and just afraid other > >> > developers may dislike the extra parameter. > >> > > >> > The race condition you mentioned is a valid concern, and I have thought > >> > about it, one way is moving the set_orig_size() after the redzone/poision > >> > setup, and in 'check_object()' we can detect whether the 'orig_size' is > >> > set, and skip that check if it's not set yet. As the manual validate_slab > >> > triggered from sysfs interface is a rare debug activity, I think skipping > >> > one object shouldn't hurt much. > >> > >> That will require smp_wmb()/smp_rmb() pair to make sure that > >> effects of set_orig_size() to be visible after redzone/poison setup. > > > > Yes, synchronization is needed here. > > > >> Isn't it simpler to add a parameter? > > > > OK, I can go this way in v5 if other developers are fine. thanks > > How about get_partial() instantiates an on-stack structure that contains > gfpflags, ret_slab, orig_size and passes pointer to that to all the nested > functions. > > Would be similar to "struct alloc_context" in page allocation. > Something like "struct partial_context pc"? Yep! This would make the parameters passing much tidier. Will try this way. More aggressively is to also embed the 'kmem_cache' parameter into it, but this may make the code look ambiguous. Thanks, Feng
